Maintained by Robin Tecon, microbiologist and postdoctoral researcher at the Swiss Federal Institute of Technology Zürich. This blog is about bacteria (and other microbes) and the scientists who study them.

Whitman and his colleagues noted that the actual total
number of bacterial cells had never been assessed, ‘because an estimation of the number of prokaryotes would seem to
require endless cataloging of numerous habitats’. It certainly seemed to me
that way, but they ended up with a convincing estimation after looking for
representative habitats in both aqueous and terrestrial environments. What is
striking is that many habitats that show very high densities of bacteria, such
as, say, animals’ gut (up to 1011 per g of human colon), account for a
negligible fraction of the total. The main crowd is apparently to be found in
subsurface sediments and terrestrial subsurface (probably >95%). Hence, what
is directly accessible to us (plants, animals, soil, oceans, lakes, etc.)
represents a mere 5% of the total bacterial environment. Talking about the tip
of the iceberg…

A couple of years ago, during a presentation of my PhD
thesis to a non-professional audience, I used some data from Whitman et al. in
a cartoon that was meant to illustrate the amazing ubiquity of bacteria on
Earth: